OP: just drill out the holes in the rad support and use some plastic pushpins to mount it, personally i believe that was a replica as a genuine subaru V7 grille would not have holes like that to mount with. I have gotten 2 genuine JDM STi grilles and neither had the holes shaped like that. Unless you can prove otherwise that it is a genuine item then it appears you got a used item with which the previous owner(s) drilled the holes to be that shape.